Wind is caused by air moving from an area of high pressure to an area of low pressure. The naturally occurring flow of air has been harnessed for centuries in order to accomplish various useful functions. For example, windmills were originally used to accomplish mechanical functions such as grinding and pumping water. Eventually windmills were used to generate electricity by coupling a generator to a rotating portion of the windmill.
In order to increase the amount of energy produced, wind-harnessing devices are placed in areas where the wind blows the strongest and the most frequently. However, one drawback of positioning wind-harnessing devices along the surface of the earth is that in most areas the wind does not always blow with enough force to generate electricity. This is due to the fact that the pressure differential along the surface of the earth is always changing. Thus, a wind-harnessing device in a fixed position on the surface of the earth is only effective when the pressure conditions along the surface of the earth are suitable to generate a flow of wind that can motivate a generator.